A runtime error is caused by an error within a program's code. This is a problem at the programmers end, not yours.
What usually happens is that you (or the software) do something unexpected and the program doesn't know how to handle it. When someone creates a piece of software, they try to anticipate every possible scenario. Unfortunately, that's next to impossible and sometimes you end up with bugs, including runtime errors.
So, what do you do if you get one of these runtime errors? Check the program's website for any updates or patches. You could also contact the program vendor and let them know the details of your problem. This could include where you are within the program when the error occurs, your version of Windows, or what other programs you have running in the background.